1. Field of the Invention
This invention relates to the destruction of organic wastes in a molten salt medium, and is particularly directed to an improved refractory for containment of molten salt such as alkali carbonate used in a reaction for oxidative destruction of fluorine-containing organic waste, and resistant to destruction from fluoride salts, particularly sodium fluoride, in the melt and produced by such reaction.
2. Description of the Prior Art
Molten salt oxidation (MSO) has been demonstrated to be a suitable technology for destroying hazardous organic wastes. The technology achieves this destruction by the catalytic oxidation of the organic compounds by molten salts at elevated temperatures. Certain of such organic wastes comprise fluorine-containing compounds such as Freons, which are chloro-fluoro methanes, and halons, which are similar to Freons but contain a mixture of bromine and fluorine atoms.
Conventional refractory bricks such as alpha-alumina bricks are employed to form the wall of molten salt reaction vessels for containing molten salts such as alkali carbonate, e.g. sodium carbonate, at temperatures of 900.degree.-1000.degree. C. Such traditional refractory bricks are based on pressed and sintered alpha-alumina. However, in the presence of even small amounts of fluoride salts, particularly NaF, present in the molten salt bath as products of the oxidation reaction of the fluorine-containing organic waste with the molten salt, the alpha-alumina readily converts to beta-alumina with a resultant destructive expansive phase change. The life of the refractories thus becomes limited.
Thus, it has been found that alpha-alumina bricks will crack and swell when in contact with sodium carbonate molten salt containing even small amounts of fluoride salts such as NaF. The fluoride does not enter into the reaction with the alumina, e.g. to form aluminum fluoride, but rather at fairly low temperatures, e.g in the 500.degree. C. temperature range, the fluorine apparently acts in some way as a catalyst to react sodium with the alpha alumina structure to form the beta-alumina structure Na.sub.2 O 11Al.sub.2 O.sub.3, with an approximate 18% volume expansion which is obviously destructive to the integrity of a solid alumina-containing brick.